The Stalker was first produced in 2594 as a heavy assault BattleMech for the Reunification War. The engineers and designers at Triad Technologies created the Stalker to be a heavily-armored weapons platform capable of handling combat at any range and absorbing a tremendous amount of punishment. Although among the slowest 'Mechs ever built, the Stalker was still fast enough to keep up with other assault 'Mechs and lead major advances, using its firepower to blast holes in the enemy's lines. Its heavy armor and armament also makes it well-suited for urban combat. Indeed a favorite tactic developed by Stalkerpilots was to lay in wait inside a building until an enemy 'Mech passes by, then crash through the wall and emerge onto the street behind them.[2][3]

For nearly two hundred years, the Stalker remained in service in the Star League Defense Force as a workhorse assault 'Mech until the fall of the Star League, where it continued in the same capacity for another two hundred years in service to the Successor States. It also remained in continuous production during this time for, when Triad Technologies was destroyed in the Succession Wars, both Irian BattleMechs Unlimited and Trellshire Heavy Industries began producing Stalkers at their factories on Shiro III and Twycross respectively. Both the Free Worlds League and Lyran Commonwealth were thus able to maintain the largest number of Stalkers in their arsenals, but still the 'Mech was so common throughout the Inner Sphere and Periphery that some pilots lost their fear of it (at least until they had to face one in combat). Its long career also led to a large number of variants, one of the most common being removing ten to fifteen tons of weaponry in order to lighten the strain on its increasingly older, battle-worn skeleton.[2][3]

Starting in the late 3040s, Irian began utilizing newly-recovered lost technology to update the original design, improving upon its weaponry and armor and increasing its heat management capabilities. These new STK-5M models were fielded in time to take part in the Clan Invasion, although even with their upgrades they were sorely tested by the Clans' OmniMechs. The Federated Commonwealth also produced their own variant, the STK-5S, although this was introduced towards the end of the invasion. New variants would continue to be produced in the wake of the FedCom Civil War, one for both of the split nations, and by Irian in an effort to further keep the design alive.[4]

The Stalker's weapons array is geared to increase damage as it closes with its target. The Stalker's long range weapons are two Jackson B5c LRM-10 launchers, one of each mounted in either "arm" with an accompanying one ton of reloads. These provide the Stalker with its longest-range punch and allow it to give indirect fire support when needed. At shorter range the Stalker next brings its two Magna Mk III Large Lasers split between left and right torso to bear on its target. For close ranges, the Stalker carries four Magna Mk II Medium Lasers split between the two arms and two Thunderstroke SRM-6 launchers, each fed by two tons of reloads, split between left and right torso.[2][3]

The number of weapons carried by the Stalker is so great that should a pilot attempt to fire them all at once they would easily overload the twenty heat sinks the 'Mech carries. Originally, the Stalker used a special fire-control computer which determined the range to the enemy and suggested the optimal mix of weapons to avoid such a problem occurring, although with the ravages of age, many older 'Mechs lack this vital piece of equipment. These pilots therefore must take care when in combat: thirteen and a half tons of armor may defend against the enemy's blows, but will do nothing to prevent an ammunition cook-off caused by overheating.[2][3]

The 3H variant of the Stalker was introduced by Triad Technologies in 2638 to take part in sieges. The 'Mech removes both large lasers and LRM-10s and replaces them with two LRM-20 launchers and two tons of reloads. This makes the 3H a powerful long range fire support 'Mech. BV (1.0) = 1,249, BV (2.0) = 1,624[3]

STK-4N

A modification of the Stalker introduced in 2876 which sought to increase its heat efficiency, the 4N model removes one of the LRM-10 launchers and adds six heat sinks to the design. These make the Stalker more heat efficient but also make the 'Mech weaker when engaging an enemy at long range. BV (1.0) = 1,225, BV (2.0) = 1,558[3]

STK-4P

In 2928, as Stalkers suffered structural weakness symptomatic of the extreme stress the 85-ton 'Mech's skeleton had to bear, this necessitated the lightening of the load by a full ten tons. The 4P was a common solution to this problem; techs simply removed a single LRM-10 in order to keep an otherwise capable 'Mech in service. BV (1.0) = 1,126, BV (2.0) = 1,417[7]

STK-5M

An upgrade originating from the Free Worlds League, the 5M variant of the Stalker was introduced in 3050 using moderate amounts of Star League technology. Most of the weaponry was retained but both large lasers were removed for a single Diverse Optics Sunbeam ER Large Laser placed in the 'Mech's centerline and a Narc Missile Beacon in the left torso accompanied by two tons of reloads, allowing the Stalker to tag enemy units with homing beacon and direct friendly missile fire onto them. The seventeen double heat sinks of the 5M afford it far greater heat efficiency than the twenty single heat sinks of previous models, although it still could not handle firing all of its weaponry simultaneously, and an additional ton of armor was added for survivability. Other changes included the use of proprietary components such as an Irian E.A.R. communications system, Riese-456 armor and a Irian Chassis Class 30. Unfortunately the designers of the new 5M dismissed the inclusion of CASE, a factor which led directly to the deaths of several Stalkers during the Clan Invasion due to ammunition cook-offs caused by overheating and weapon penetrations. BV (1.0) = 1,316, BV (2.0) = 1,655[4]

STK-5S

Outfitted with the relatively recently rediscovered Star League technology of circa 3050, the FedCom 5S can be characterized primarily by its tendency to overheat. The designers behind this variant took the simple expedient of upgrading its engine and firepower without taking heat build-up into consideration. The 'Mech has had its engine replaced with an XL Engine and the large lasers have been removed and replaced with two Large Pulse Lasers. For protection against ammunition explosions, CASE has been added to both side torsos, and an Anti-Missile System has been added for protection against incoming missiles. BV (1.0) = 1,009, BV (2.0) = 1,423[8]

STK-6M

Irian’s attempt to make up for the shortcomings of the 5M, the 6M introduced in 3062 drops the SRMs entirely, upgrades the LRMs to 15-tube racks with integral Artemis IV FCS, and upgrades the lasers to ER versions, mounting a fifth medium. Most importantly, the LRM magazines are now protected with CASE. BV (1.0) = ?, BV (2.0) = 2,029[8]

STK-7D

The 7D Stalker introduced by the Federated Suns in 3062 is built on a standard chassis and engine for rugged durability and carries a primarily energy arsenal. Its two primary weapons are two ER PPCs, giving the 7D a striking distance out to just under seven hundred meters. The 'Mech is also armed with four Medium Pulse Lasers for close combat, which are backed up by two Streak SRM-4 launchers to take advantage of any weak points in an enemy's armor. The lasers and ER PPCs are all linked to an advanced Targeting Computer, which gives the 7D extreme accuracy. BV (1.0) = 1,533[9], BV (2.0) = 1,901[8]

Designed for close combat, the Stalker used by Sho-sho Jagawen Torisobo in 3028 replaced the LRM launchers with an additional SRM-6 rack in each torso. Six additional heat sinks kept the machine cool. BV (2.0) = 1,570[12]